This project investigates the biological and physicochemical properties of a unique class of powerful immunological adjuvants. These compounds, which are surface active agents, appear to act via a previously unsuspected mechanism that involves an ability to form multivalent binding sites on hydrophobic surfaces. We tested the ability of 17 large hydrophobic surfactants to enhance antibody formation and inflammation. The surfactants were all block copolymers of 10 or 20% hydrophilic polyoxyethylene (POE) and the rest hydrophobic polyoxypropylene (POP). They differed in molecular weight and mode of linkage of POP to POE. Each of the 17 agents produced a distinct pattern of immune response and inflammation. For example, surfactants with 10% POE and the structure POE-POP-POE were effective adjuvants for antibody formation and produced moderate inflammation at the site of injection. Those with similar composition but the reverse structure of POP-POE-POP were poor adjuvants but produced severe inflammation. One of these which has a structure reminiscent to the mycobacterial glycolipid trehalose 6-6' dimycolate suppressed immune responses and stimulated thymic hyperplasia. The hypothesis that this compound is a selective adjuvant for suppressor cells is being investigated. A better understanding of the nature of adjuvants that selectively stimulate effector or suppressor responses may be of value in several areas of cancer biology. (TA)